Thanks for the advice. So, bookworm-updates is recommended, bookworm-backports is optional. At upgrade time the documentation said something else (I suppose, because it was an upgrade no fresh installation) Well, the problem is solved. Thanks for the hint. Best Hans > So, should I use all four entries or do you recommend to skip one of it? > > https://wiki.debian.org/SourcesList > > Cheers, > David.